Method of manufacturing coil springs



Oct. 29, 1940.

L. A. YOUNG El AL METHOD OF MANUFACTURING COIL SPRINGS Filed Nov. 13, 1939 M, ATTO NEy- Patented Oct. 29,1940

PATENT OFFICE METHOD OF MANUFACTURING COIL SPRINGS Leonard A. Young, Detroit, Mich., Hubert B.

Hathaway, Windsor,

Ontario, Canada, and

Bernard Hellman, Detroit, Mich; saidHathaway and said Hellman assignors to said Young Application November 13, 1939, Serial No. 304,090

4 Claims.

The present invention relates to a novel meth-- od of forming resilient spring members, such for example as coil springs or the like, from relatively non-resilient materials such, for example, I as so-called steel spring wire stock. The particular improvement of the present method resides in the provision of means for heat treating the material of which the springs are formed before it is formed into springs. The invention may also, if desired, be adapted to the tempering, annealing or other heat treatment of spring wire stock either of so-called low carbon or high carbon" steel.

Prior to the present invention it was customary to provide for the heat treatment of the formed .resilient spring members to secure a tempering or normalizing of the wire in the finished spring member.

While the terms tempering, annealing and normalizing" are used somewhat loosely in this art, the terms as used herein are intended to designate any heat-treating operation which has for its purpose or effect the elimination of stresses and strains in the wire due to either the wire-drawing or the spring-forming operations, to impart the desired strength and resiliency characteristics to the spring.

Prior to the present invention it was common practice to treat the formed springs by heating 'them in an oven where they were subjected to a predetermined temperature for a predetermined period of time to impart the desired characteristics to the springs. It was common practice to place the springs in baskets and pass them through the oven by a suitable conveyor mechanism. In the use of this method of heat treatment of the springs it was difficult to control the heat treatment of the completed springs, and the operation was further complicated in that the 40 springs which may be treated in the oven at any one time may be of different sizes and different shapes. This makes it difficult to assure uniform treatment of the springs of the various kinds slnce'the effect of the heat on the springs varies with the amount of metal which has been used in the forming of the spring, and the time that the spring is in the oven. Thus a spring of small gauge wire subjected to the same heat treatment as a larger spring of heavier gauge wire will not 50 be satisfactorily heat treated and vice versa.. The heating of the springs in such oven caused the metal of the springs to expand and caused the springs to become very badly entangled with each other so that a large amount of unproductive time was required for the purpose of disentangling the springs after they had been subjected to the heat treatment.

While the present invention is concerned primarily with the treatment of coil springs, it is to be understood that the invention is also applicable to other types of springs as well as to the treatment of metallic objects which are not formed as springs. The term springs as used herein is thus intended to refer to any type of metallic spring members.

It is therefore an important object of the present invention to provide a novel method of manufacturing springs wherein the material of which the springs are formed is subjected to normalizing, annealing or tempering heat treatment before being formed into springs.

A further object of the invention is to provide a method of manufacturing springs particularly but not exclusively adapted to the manufacture of coil springs from steel wire stock and in which the material forming each spring is progressively heat treated under controlled conditions prior to its formation into springs whereby uniformity of size, strength and resiliency of the springs is achieved rendering the method economical and practical to carry out in production on a commercial scale.

Another object of the invention is to subject the wire or other material of which springs are formed to a heat-treating operation whereby it is in a heated condition, in which the strains therein are substantially normalized at the time the wire passes to the forming members of the spring forming machine.

Yet another object is to provide aspring formed of preheat-treated material wherein the stresses in the spring are normalized upon cooling after passing through the forming rolls.

A still further object is to provide a spring wherein the material of which the spring is formed is free from scale formation, and is highly resistant to rust and corrosion.

Another object is to provide an improved method of forming springs wherein the grain structure of the material of which the spring is formed is substantially the same as the grain structure of the material before being formed into the spring.

Yet a further object resides in the provision of a novel method of economically manufacturing coiled springs in an improved manner whereby the stresses in the material of which the springs are formed are uniformly distributed.

Other objects and advantages of this invention will be apparent from the following detailed description considered in connection with the accompanying drawing in which:

"Fig. l is a side elevation of a machine, somewhat diagrammatic in nature, embodying the method of thepresent invention; and

Fig. 2 is a fragmentary side elevation of a modified form of the machine shown in Fig. 1.

Before explaining in detail the present'invention it is to be understood that the invention is not limited in its application to the details of construction and arrangement 'of parts illustrated in the accompanying drawing, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation, and that it is not intended to limit the invention claimed herein beyond the requirements of the prior art.

The method of the present invention consists essentially in forming metallic spring members, in the embodiment here disclosed these being coil spring members formed from steel wire spring stock, and comprises heating the material from which the spring is to be formed, preferably by electrical resistance heating, until the desired annealing, normalizing or tempering of the metal forming the spring is completed, and thereafter passing the heated material to the forming rolls of the spring forming machine to form the spring and then permitting the material of the spring to cool to atmospheric temperatures.

The improved method of forming springs is shown by way of example in the somewhat diagrammatic figures of a machine shown in the accompanying drawing. In carrying out this method steel wire or other suitable spring forming stock I0, preferably containing carbon within the range of approximately 50% to .70%, is placed on a reel I2 supported on a standard M. The wire '10 is withdrawn from the reel I2 and is passed through an electrical heating device 16 having spaced electrodes 18 and 20 which may be the multiple contact type shown in Fig; 1, which are electrically connected with a transformer which delivers electrical energy. If desired, the electrodes may be of a rotary type such as that shown in Fig. 2 and in which a plurality, in the present instance four, of spaced electrodes 40 are mounted on an electrically insulated rotor 4| and electrically connected through brushes t2 and suitable circuits, including a transformer,

with the source of electrical energy. The electrodes 40 are arranged to contact the surface of the wire l0 and electric current flows therefrom through the wire ID to the roller 43 which is grounded.

The electrical energy employed with either type of electrode is preferably of the alternating current type of 60 cycles or higher and of either or 220 volts reduced through the transformer to voltages within the range of approximately 6 to 40 volts. It is believed that current of higher frequencies and either lower or higher voltages may be used advantageously and therefore we do not desire to be limited to the current frequencies and voltages specified herein.

After the wire I!) passes through the electrodes l8 and 20 or the rotary electrodes 40, it is passed through a wire straightening mechanism 22 and thereafterpasses through feed rolls 24 and 26 respectively to a forming die 28 of a conventional type of spring forming machine. The wire I0 is coiled by contact with the forming die 28 and a spring is formed by rolling spaced convolutions of the wire in substantially predetermined spaced relation. When the desired number of convolutions has been formed to produce a spring of the desired type, the wire I0 is cut by a cut-off mechanism 30 and the completed 5 spring indicated at 32 rolls down a ramp 34 mounted on suitable supports 36.

The wire I0 is preferably formed of steel having a carbon content ranging from between 50% to approximately 370%. The spacing of the electrodes l8 and Z0 and the spacing of the electrodes 40 and the speed of revolution of the rotor 4|, together with the speed of the wire and the intensity of the electric current, control the amount of heat developed in the wire In during its contact with said electrodes. As the wire I0 progressively moves toward the forming die 28, difierent portions of the wire are continuously J brought into contact with the electrodes whereby the entire wire is progressively heated to desired 20 temperatures prior to the time that it is brought into contact with the forming die 28.

The wire In is preferably heated by the electrodes to such a degree that the wire will be delivered to the forming die 28 when at a temperature of approximately 475 to 575 F. In view of the fact that the wire l0 moves quite rapidly, very little heat is lost as the wire passes through the wire straightening mechanism and between the feed rolls 24 and 26 respectively. The spacing of the electrodes and the speed of travel of the wire and the intensity of the electric current can be regulated accurately so as to develop the desired temperature in the wire at the time it passes to the forming die 28. The heat developed in the wire should be suflicient to normalize the strains in the wire and to properly anneal or heat treat the wire after it passes through the forming die 28.

It has been found that the lower the carbon content of the wire subjected to heat treatment. the higher the current consumption required to develop a given temperature in the wire in a givenperiod of time, and the higher the carbon content the lower the current consumption required to develop a given temperature in the wire in a given time. As will be readily appreciated it is easy to accurately control the heat treating of the wire to insure that the wire be passed to the forming die 28 at the proper temperature consistent with the carbon content of the particular material being used, and the diameter of the wire l0, which varies in, springs of different size. If desired, thermocouples may be employed to register the temperature of the wire at various points and to actuate controls for regulating the speed of operation of the machine.

While the scientific phenomenon underlying the present invention is in part unknown to us. we believe that the results achieved in carrying out the present invention are due in part to a molecular rearrangement affecting the crystalline structure of the material of the wire It. In view of the fact that metal such as steel is a dispersion of crystalline particles in a dispersion medium which is solid at normal atmospheric temperatures, the heating of such metals tends to decrease its resistance to plastic flow and to permit a more ready rearrangement of the crystals therein. The size and shape of the crystal line particles, together with the distribution of the crystalline particles in the dispersion medium, determine the physical characteristics of the material in the formed spring 32.

It is our belief that the heating of the wire 7 or other metal stock, prior to the spring forming operation, to a point where the resistance of the metal to plastic flow at normal atmospheric temperatures is reduced, causes the metal to more readily adapt itself to the shape imparted to it by the spring forming machine. At the same time the heating by the use of alternating electric current subjects the internal structure of the metal to pulsations of electric current flow which alternate in direction through the wire I0. In other words, since as the name implies, the current alternates between negative and positive poles and is reversed, in the preferred instance 60 or more times per second, it will beseen that the crystalline particles are subjected to the driving force of the electric current in rapidly alternating directions.

It isour belief that this tends to cause the particles of which the wire is formed'to move in their heated dispersion medium to such an extent that the crystalline particles rubbing against each other and against the matrix tend to assume a generally uniform size and shape which results in a more uniform structure of the metal. This rapidly alternating flow of electric current also tends to assure a more uniform distribution of the particles in the mass. Photomicrographs of the metal stock of wire ill have been taken both before and after being formed into-springs 32. These photomicrographs show that springs formed by our improved method embody a more uniform size and shape of crystalline structure in the steel, and also a more equal dispersion of the particles in the matrix than are present in springs formed by other methods.

While the flow of electric current through the wire tends to impart a slight magnetic property to the wire during the heat treatment, it is not as magnetic as would be the case if treated with direct current, and this slight magnetism is readily dissipated.

It has also been found that springs formed by our improved method are more highly resistant to rust, and are not nearly so susceptible to scale formation as are springs formed and heat treated by conventional methods. The metal of the completed springs 32 apparently possesses the same grain structure as it possesses in the uncoiled condition. The result is that the springs last longer in service and exhibit a more uniform distribution of stresses than do springs formed by other methods.

The springs formed by our improved method may be manufactured more economically and can be handled easier because of the fact that there is no tendency for the springs to expand and to coil around each other as the! cool because the springs are delivered from the forming die 28 individually. I

It is our belief that the high degree of resistance of the completed springs to rust and corrosion is due in part to the more uniform distribution of the crystalline particles in the spring and in part to the more uniform size of these particles which eflect a reduction of size of the inter-crystalline or inter-particle spaces on the surfsceofthespring. Y

It is to be understood that we do not desire to be limited by the foregoing statements of our belief as to the scientific phenomenon underlying the present invention. We do not desire to be limited to the particular sequence of steps herein disclosed as a preferred embodiment of the invention because various changes may be made without departing from the spirit of the invention; for instance, the wire straightening mechanism 22 may if desired be interposed between the heating device .l6 and the reel II.

We claim:

1. The method of forming coil springs which comprises passing steel wire stock through a heating element comprising a plurality of spaced electrodes electrically connected with a source of electrical current adapted to subject said stock to the flow of alternating electrical current of approximately 60 cycles at voltages within the range of approximately 6 to 40 volts thereby to heat the stock to temperatures within the range of approximately 475 to 575 F., thereafter passing the heated stock successively through a straightening device and forming rolls, and then forming said heated stock into coil springs.

2. The method of forming springs which comprises the steps of connecting successive portions of spring wire stock as resistance heating elements in an electrical circuit and causing the flow of 60 cycle alternating electric current at voltages within the range of approximately 6 to 40 volts to create temperatures in said wire within the range of approximately 475 to 575 1''. to normalize the strains therein and to reduce the resistance of said stock to plastic flow, and thereafter forming said wire into springs while in such heated condition.

3. The method of forming springs which comprises the steps of connecting successive portions of spring wire stock as resistance heating elements in an electrical circuit and causing a flow of 60 cycle alternating electric current at voltages within the'range of approximately 6 to 40 volts to create temperatures in said wire within the range of approximately 475 to 575 F. to normalize the strains therein and to anneal the stock and to reduce the resistance of said stock to plastic flow, rolling the stock' while in such heated condition to form springs, and severing the formed springs from the heated stock.

4. The method of forming steel coil springs from steel stock containing carbon within the range of approximately .50% to .70% which comprises subjecting the metal stock to continuous heating by passing an electrical circuit therethrough and causing a flow of 60 cycle alternating electric current at voltages within the range of approximately 6 to 40 volts to heat said metal stock to a desired temperature within the range of approximately 475 to 575 F. to anneal said-stock and reduce its resistance to plastic flow, and thereafter passing said stock while heated through a spring forming machine.

LEONARD s. YOUNG. BERNARD nnnsum. nnmm'r B. HATHAWAY. 

